Apache SpamAssassin is an extensible email filter
that is used to identify spam. Once identified,
the mail can then be optionally tagged as spam for
later filtering. It provides a command line tool
to perform filtering, a client-server system to
filter large volumes of mail, and
Mail::SpamAssassin, a set of Perl modules allowing
Apache SpamAssassin to be used in a wide variety
of email systems.

Gtk2-Perl is the collective name for a set of Perl bindings for GTK+ 2.x and various related libraries. These modules make it easy to write GTK+ and GNOME applications using a natural, perlish, object-oriented syntax.

Xapian is a search engine library, scalable to collections containing hundreds of millions of documents. It's written in C++ with bindings for Perl, Python, PHP, Java, Tcl, C#, Ruby, and Lua. It is a highly adaptable toolkit that allows developers to easily add advanced indexing and search facilities to their own applications. It supports the Probabilistic Information Retrieval model and also a rich set of boolean query operators. Omega is a Web search application built upon the Xapian library. It can index a Web server's document tree (including HTML, PDF, OpenOffice, MS Word/Excel/Powerpoint/Works, WordPerfect, RTF, PS, etc.), or data exported from arbitrary sources (e.g. SQL databases).

metaf2xml can download, parse, and decode aviation routine weather reports (METAR, SPECI, SAO), aerodrome forecasts (TAF), synoptic observations (SYNOP), and BUOY observations, and store the data as XML. XSLT style sheets convert it to plain language, as HTML or text. Current weather data from NOAA and other sources can be fetched and displayed.

Libev is a high-performance event loop for C (with optional and separate interfaces for C++ and Perl), featuring support for I/O, timers (relative and absolute, cron-like ones), signals, process status changes, and other types of events. It has both a fast native API and libevent emulation to support programs written using the libevent API. Differences to libevent include higher speed, simpler design, more features, less memory usage, embedability, and no arbitrary limits. libev supports epoll, kqueue, Solaris event ports, poll, and select.

svk is a distributed version control system
designed from the ground up to integrate cleanly
with Subversion, the emerging standard in
enterprise version control. With SVK, advanced
branching and merging and even offline commits are
easy.

Config-Model provides a framework for editing and validating the content of any configuration file or data. With a configuration model (expressed in a data structure), Config-Model provides a user interface and a tool to validate configuration. An optional graphical (Perl/Tk) or curses interface can be used to edit configuration data that will be validated according to the user-provided model. Config-Model includes a model example for fstab and a small fstab demo.

HTML::Mason is a full-featured web site development and delivery system. Mason allows web pages and sites to be constructed from shared, reusable building blocks called components. Components contain a mix of Perl and HTML, and can call each other and pass values back and forth like subroutines. Components increase modularity and eliminate repetitive work. HTML::Mason is most powerful when used in conjunction with mod_perl, but can be used in standalone applications as well.

qpsmtpd is a flexible smtpd daemon written in
Perl. Apart from the core SMTP features, all
functionality is implemented in small "extension
plugins" using the easy-to-use object oriented
plugin API. qpsmtpd was originally written as a
drop-in qmail-smtpd replacement, but now it also
includes an smtp forward and a postfix "backend".